Expansion on what is Wind Energy?
Ending on the wind resource
• All renewable energy (except tidal and geothermal power),
ultimately comes from the sun
• The earth receives 1.74 x 1017 watts of power (per hour) from the
• About one or 2 percent of this energy is converted to wind
energy (which is about 50-100 times more than the energy
converted to biomass by all plants on earth
• Differential heating of the earth’s surface
and atmosphere induces vertical and horizontal
air currents that are affected by the earth’s
rotation and contours of the land WIND.
~ e.g.: Land Sea Breeze Cycle
• Winds are influenced by the ground surface at altitudes up to
• Wind is slowed by the surface roughness and obstacles.
• When dealing with wind energy, we are concerned with
• A wind turbine obtains its power input by converting the
force of the wind into a torque (turning force) acting on the
• The amount of energy which the wind transfers to the rotor
depends on the density of the air, the rotor area, and the wind
• The kinetic energy of a moving body is proportional to its
mass (or weight). The kinetic energy in the wind thus depends
on the density of the air, i.e. its mass per unit of volume.
In other words, the "heavier" the air, the more energy is
received by the turbine.
•Therefore the wind energy is the most important renewable
resource on the Earth.
A Windmill captures
wind energy and then
uses a generator to
convert it to electrical
• The design of a
windmill is an integral
part of how efficient it
• When designing a
windmill, one must
decide on the size of
the turbine, and the
size of the generator.
Able to deliver electricity at lower cost
than smaller turbines, because
foundation costs, planning costs, etc.
are independent of size.
Well-suited for offshore wind plants.
In areas where it is difficult to find sites,
one large turbine on a tall tower uses
the wind extremely efficiently.
Local electrical grids may not be able to handle the large electrical
output from a large turbine, so smaller turbines may be more
High costs for foundations for large turbines may not be
economical in some areas.
• (1) A wINd TUrbINE CApTUrEs ENErgy from
movINg AIr ANd CoNvErTs IT INTo ElECTrICITy.
• CApTUrEd ENErgy Is AffECTEd by fACTors
sUCH As AIr dENsITy, TUrbINE swEpT ArEA,
• vEloCITy ANd powEr CoEffICIENT As IN THE
followINg EQUATIoN .
• (2)A mATlAb/sImUlINk modEl Is dEvElopEd To
sHow How wINd ENErgy gENErATEd powEr
from wINd TUrbINE.
THE WIND RESOURCE
• The wind resource–how fast it blows, how often, and when–plays a significant
role in its power generation cost. The power output from a wind turbine rises
as a cube of wind speed. In other words, if wind speed doubles, the power
output increases eight times. Therefore, higher-speed winds are more easily
and inexpensively captured.
• Wind speeds are divided into seven classes–with class one being the lowest, and
class seven being the highest. A wind resource assessment evaluates the
average wind speeds above a section of land (e.g. 50 meters high), and assigns
that area a wind class. Wind turbines operate over a limited range of wind
speeds. If the wind is too slow, they won't be able to turn, and if too fast, they
shut down to avoid being damaged. Wind speeds in classes three (6.7 – 7.4
meters per second (m/s)) and above are typically needed to economically
generate power. Ideally, a wind turbine should be matched to the speed and
frequency of the resource to maximize power production.
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